Arm pipe for record player tonearms

ABSTRACT

An arm pipe for a record player tonearm comprises a composite material essentially consisting of a thermoplastic resin and graphite powder. The composite material is prepared by kneading the components, rolled to impart a degree of orientation to the graphite powder particles, which are in the form of flaky graphite and then molded into a pipe, along the surface of which the graphite particles are oriented. Arm pipes wherein the composite material is oxidized at the surface of the pipe and arm pipes wherein the composite material is carbonized or graphitized are also included. A light weight, rigid arm pipe having a high specific modulus of elasticity is obtained through a simple procedure at low cost.

BACKGROUND OF THE INVENTION

This invention relates to arm pipes for record player tonearms.

The recent trend of tonearms for record players is directed toward areduction of the mass and an increase of the compliance of a vibrationsystem in order to enhance the trackability of a cartridge.

With the compliance of a cartridge increased, the low range reasonancefrequency attributable to the cartridge compliance and the equivalentmass of a tone arm (including the cartridge) at the stylus tip isreduced such that noise signals due to warpage and eccentricity of arecord may be often picked up. That is, the increased compliance resultsin a reduced signal-to-noise ratio. It is therefore necessary to adjustlow range resonance to an inoffensive level, generally to a range of 10to 15 hertz while the stylus equivalent mass is kept low.

To reduce the equivalent mass at the stylus tip, in usual practice,tonearm component parts such as arm pipe and head shell may be reducedin weight. Parts having a wall thickness reduced for light weightexhibit a low rigidity which in turn, allows undesirable phenomena suchas partial vibration to occur, resulting in deteriorated sound quality.To obtain light weight arm pipes and head shells having a high rigidity,materials are required having a high specific modulus of elasticity.

In prior art arm pipe and head shell manufacture, aluminum and titaniumare used because they have a relatively high specific modulus. However,the use of a cartridge with an increased compliance requires the armpipes and head shells to be made of material having a higher specificmodulus than aluminum and titanium.

Arm pipes and head shells made of fibrous carbon are known. Fibrouscarbon itself has a sufficiently high specific modulus while it cannotbe formed into a part without a binder. Usually, resin is used to bindfibrous carbon. However, the addition of a resin binder to fibrouscarbon causes the specific modulus of elasticity to reduce to a levelequal to or less than those of aluminum and titanium. Therefore, thefibrous carbon composite material is not satisfactory as the materialfor arm pipes and head shells.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a highperformance arm pipe made of a light weight, rigid composite materialhaving a high specific modulus of elasticity.

According to one aspect of this invention, there is provided an arm pipefor a tonearm of a record player which comprises a composite material ofa thermoplastic resin and graphite powder. The material is obtainedsimply by kneading the components and the graphite powder particles areoriented substantially in parallel with the surface of the pipe.

According to another aspect of this invention, the material in the formof a pipe is oxidized at least at the surface of the pipe. The materialmay also be carbonized.

To provide the graphite powder particles with a substantial degree oforientation, the kneaded mixture may preferably be rolled into a sheetand the sheet is then formed into a pipe.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in further detail by referring tothe accompanying drawings wherein:

FIG. 1 is a partial cross-sectional view of a mixture of graphiteparticles and a resin matrix;

FIG. 2 is a partial cross-sectional view of a sheet of a compositematerial wherein graphite particles are oriented in a resin matrix;

FIG. 3 is an axial cross-sectional view of the arm pipe of theinvention;

FIG. 4 is a cross-sectional view of the arm pipe taken along the lineIV--IV in FIG. 3; and

FIG. 5 is a schematic view of a tonearm system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The thermoplastic resins used herein include polyvinyl chloride,polyvinylidene chloride, vinyl chloride-acrylonitrile copolymers,vinylidene chloride-acrylonitrile copolymers, vinyl chloride-vinylacetate copolymers, etc., and mixtures thereof. The resins may bechanged into a pitch-like state by dry distillation before it is kneadedwith graphite powder according to this invention.

The graphite powder is available from many manufacturers. Flaky graphitepowder is most preferable. The graphite powder may preferably have anaverage particle size of less than 20 microns (inclusive), particularly0.1 to 5 microns.

The weight ratio of resin to graphite varies from 1:9 to 9:1, preferably3:7 to 7:3.

An example of this invention is shown below. Polyvinyl chloride (to beabbreviated as "PVC" hereinafter) is used as a typical thermoplasticresin. In a kneader, 30 parts by weight of PVC is blended and kneadedwith 70 parts by weight of graphite powder at a temperature of 130°-200°C. The green intimate mixture is further mixed and rolled into a sheetat a similar temperature. This sheet exhibits a Young's modulus E of6,000 kg/mm² (5.9×10¹⁰ N/m²) and a density of ρ of 1.8 g/cm³. Thespecific modulus of elasticity calculated in terms of √E/ρ is 5.7×10³m/sec, which value is higher than the specific modulus of titanium of5.2×10³ m/sec. The green, but oriented sheet is formed into a pipethough the following description omits this process for the purpose ofillustrating measured values.

The rolled sheet is then subjected to presintering or oxidation bygradually heating it in an oxidizing atmosphere to a temperature of100°-500° C., preferably 250°-300° C. at a rate of 1°-10° C./hour. Theoxidized product has a Young's modulus E of 9,000 kg/mm², a density ρ of1.8 g/cm³ and a specific modulus √E/ρ of 7.0×10³ m/sec.

The oxidized sheet is further subjected to carbonization orgraphitization by heating it in a non-oxidizing atmosphere or in vacuumto a temperature of about 1200° C. or higher at a rate of 10°-20°C./hour. The carbonized sheet exhibits a Young's modulus E of 16,000kg/mm² and a density ρ of 1.8 g/cm³. The specific modulus of elasticityof 9.33×10³ m/sec is about 2 times higher than those of aluminum andtitanium. Graphitization of the sheet at about 2500° C. increases theYoung's modulus 1.5 times to 24,000 kg/mm².

Orientation of graphite powder particles is essential to achieve theabove-illustrated desired values. When PVC is kneaded with graphitepowder and the resulting green mixture is formed into a desired shape byextrusion, for example, without an orientation procedure, the resultingproduct shows a poor Young's modulus. By way of example, when 30 partsof PVC was kneaded with 70 parts of graphite powder and the mixture wasthen extrusion molded by means of an extruder into a plate, the plateshowed a Young's modulus of about 1,300 kg/mm². This value is less thana quarter of that of the graphite-oriented sheet described above.Further carbonization of this non-oriented plate resulted in a Young'smodulus of about 4,000 kg/mm², which value is about 1/6 of that of thegraphite-oriented one after carbonization.

Further, it has been found that the internal loss (tan δ) of thecomposite material according to this invention is higher than those ofaluminum and titanium. The higher the internal loss, the lessundesirable resonance is liable to occur.

The measurements of various properties show that the composite materialof this invention has a relatively light weight, a high rigidity, a highspecific modulus of elasticity, and a good internal loss.

As described above, to fabricate an arm pipe without impairing thecharacteristics of the composite material according to this invention,graphite powder particles must be oriented in the resulting arm pipe. Inthis respect, extrusion molding which is generally used in prior art armpipe manufacture is not applicable because graphite particles are notsubstantially oriented so that molded products are less rigid.

Referring to FIG. 1, a fragmental portion of a kneaded or intimatemixture is shown wherein a resin matrix 1 contains graphite flakes 2 atrandom. The graphite particles in the form of a flake may be consideredas a disc having a high ratio of diameter to thickness. The intimatemixture shows a random distribution of graphite flakes 2 in the resinmatrix 1.

The intimate mixture is then rolled into a sheet at elevatedtemperatures by means of rollers, presses or the like. FIG. 2 shows arolled sheet 3 wherein graphite flakes 2 are oriented in parallel withthe surface of the sheet 3. Rolling is a typical, but non-limitingtreatment for imparting a substantial degree of orientation to graphiteparticles. The thickness of the sheet 3 may suitably be selected inaccordance with a desired wall thickness of an arm pipe.

Thereafter, the sheet 3 is rounded into a pipe of a desired diameterunder high temperature and pressure conditions as shown in FIGS. 3 and4. The opposite ends of the sheet may be joined at an interface 4 in anysuitable manner as by thermal pressure bonding or by applying anadhesive. A pipe may also be fabricated by wrapping the sheet in theform of an elongated narrow tape around a core in a spiral manner.Alternatively, two sheets may be placed at the opposite sides of acylindrical core and then press or compression molded at elevatedtemperatures. The pipe may be fabricated to a given length of arm pipeor a long cylindrical product may be cut to a given length. In eithercase, graphite particles are oriented in parallel with the surface ofthe arm pipe as shown in FIGS. 3 and 4. There is obtained a rigid armpipe.

After the arm pipe 5 shown in FIGS. 3 and 4 is formed, it is subjectedto pre-sintering or oxidation by heating it in an oxidizing atmosphereto a temperature of about 250° C. at a rate of 1°-10° C./hour. Further,the arm pipe is subjected to carbonization or graphitization by heatingit in a non-oxidizing atmosphere to a temperature of 1200° C. at a rateof 10°-20° C./hour. The rigidity of the arm pipe is increased bycarbonization while the internal loss is reduced in proportion.

The arm pipe 5 is susceptible to deformation during the pre-sintering oroxidation step. Therefore, the arm pipe should be supported in asuitable manner, for instance, by inserting a core (made of material notdeformable at a temperature above 250° C.) into the bore of the pipe, orby enclosing the pipe within a support sheath. Since the pipe becomesself-supporting after the oxidation, no support is required duringcarbonization.

The carbonization temperature may be higher than 1200° C. The arm pipegraphitized at a temperature of 2,500° C. is 1.5 times higher inrigidity than that carbonized at a temperature of 1,200° C.

FIG. 5 shows an entire tonearm system. The arm pipe 5 of this inventionhas a head shell 6, which may be fabricated of the same material as thearm pipe, and a counter weight 7 mounted at opposite ends, and issupported by an arm support 8.

A sample was prepared by blending and kneading a polyvinylchloride-polyvinyl acetate copolymer and graphite powder at a weightratio of 1:2. The resulting intimate mixture was rolled to achieve asubstantial degree of orientation of graphite. Measurement was madeafter rolling, oxidation, and carbonization. The results are tabulatedbelow.

                  TABLE                                                           ______________________________________                                                                Specific                                                           Young's    modulus                                                ρ(g/cm.sup.3)Density                                                                   E (kg/mm.sup.2)modulus                                                                   ##STR1##    tan δloss                          ______________________________________                                        Rolled  1.8      6,000       5.7 × 10.sup.3                                                                   0.05                                    Oxidized                                                                              1.8      9,000       7 × 10.sup.3                                                                     0.02                                    Carbonized                                                                            1.8      16,000      9.33 × 10.sup.3                                                                  0.015                                   Aluminum                                                                              2.7      7,400       5.18 × 10.sup.3                                                                  0.003                                   Titanium                                                                              4.4      12,000      5.22 × 10.sup.3                                                                  0.003                                   ______________________________________                                    

As understood from the foregoing, the orientation of graphite powderparticles in the resinous matrix in a direction substantially parallelwith the surface provides a light weight arm pipe having a highrigidity, that is, an arm pipe having a low equivalent mass at thestylus tip. Such an arm pipe tends to pick up few noise signals due towarpage and eccentricity of a record and ensures reproduction at animproved S/N ratio when used in combination with a high compliancecartridge. The arm pipe of the invention has an internal loss such thatundesirable resonance or partial vibration may not occur. Further, thecomposite material is readily prepared by kneading relativelyinexpensive starting components, orientation is imparted by rolling orother suitable treatments, and the material is formed by a conventionalmethod. These factors contribute to a reduction of cost.

Although the present invention has been described in some detail by wayof illustration and example for purposes of clarity of understanding, itwill, of course, be understood that various changes and modificationsmay be made in the form, details, and arrangements of the parts withoutdeparting from the scope of the invention as set forth in the followingclaims.

What is claimed is:
 1. An arm pipe for a record player tonearmcomprising a composite material essentially consisting of 10-90 parts byweight of a thermoplastic resin and 90-10 parts by weight of flakygraphite wherein the composite material is prepared by kneading thecomponents and the graphite flakes are oriented substantially inparallel with the surface of the shell.
 2. An arm pipe according toclaim 1, wherein said composite material is oxidized at least at thesurface of the pipe.
 3. An arm pipe according to claim 1, wherein saidcomposite material is carbonized.
 4. An arm pipe according to claim 1,wherein said pipe is fabricated by kneading the components, rolling thekneaded mixture into a sheet to achieve a substantial degree oforientation of the graphite flakes, and then forming the sheet into ahollow cylinder.
 5. An arm pipe according to any one of claims 1 to 3,wherein said thermoplastic resin is selected from the group consistingof polyvinyl chloride, polyvinylidene chloride, vinylchloride-acrylonitrile copolymers, vinylidene chloride-acrylonitrilecopolymers, vinyl chloride-vinyl acetate copolymers, and mixturesthereof.
 6. An arm pipe according to any one of claims 1 to 3, whereinsaid graphite flakes have a particle size of 0.1 to 20 microns.
 7. Anarm pipe according to claim 6, wherein said graphite flakes have aparticle size of 0.1 to 5 microns.
 8. An arm pipe according to claim 1,wherein said composite material includes 30 to 70 parts by weight ofsaid thermoplastic resin and 70 to 30 parts by weight of said flakygraphite.